A wealth of information regarding beneficial leishmania immune responses has been acquired through the investigation of murine infection models and human patient material. These studies have clearly shown that the TH1 subset of CD4+ T cells are important for recovery from disease. But very little is known regarding the mechanisms of immunity required for successful immunization. There is evidence that in addition to Th1 CD4+ cells, the activation of other immune effector cells may be important. To develop an effective vaccine against leishmania, this issue must be addressed. Although difficult, the most useful information will be obtained by directly assessing the induction of parasite-specific responses in a human system. This proposal focuses on T cell responses induced by in vitro immunization of normal human T cells with different parasite antigen preparations including L. amazonensis infected macrophage and parasite lysate. The effects of infection versus immunization on responding T cell populations will be assessed in the context of different HLA phenotypes. The responding T cell populations will be evaluated by antigenic specificity, cell surface marker expression, profiles of cytokine production, cytolytic activity, and TCR usage to assess beneficial or pathogenic responses. In addition, cytokines and other immunomodulators will be used to drive parasite specific T cells with selected phenotypes. The emphasis is on the induction of beneficial parasite-specific human T cells which will be used to characterize mechanisms and antigens required for successful immunization. In addition, in vivo murine immunization systems will be used to complement the in vitro human studies.